Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Also, Functional Electrical Stimulation (FES) systems such as the Freehand system by NeuroControl (Cleveland, Ohio) have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Each of these implantable neurostimulation systems typically includes one or more stimulation leads implanted at the desired stimulation site and an implantable neurostimulator, such as an implantable pulse generator (IPG), implanted remotely from the stimulation site, but coupled either directly to the stimulation leads or indirectly to the stimulation leads via one or more extension leads in cases where the length of the stimulation leads is insufficient to reach the IPG. In some cases, the extension leads may be used to facilitate coupling of the neurostimulator, which may otherwise be incompatible with the stimulation leads or extension leads, thereto. Thus, electrical pulses can be delivered from the neurostimulator to the stimulation leads to stimulate the tissue and provide the desired efficacious therapy to the patient.
If the stimulation leads are to be directly connected to the neurostimulator, the proximal ends of the stimulation leads can be inserted into a connector of the neurostimulator, such that the terminals located at the proximal ends of the stimulation leads are coupled to corresponding electrical contacts within the connector. Individual wires are routed though each stimulation lead to connect the proximally-located terminals with the distally-located electrodes.
If the stimulation leads are to be indirectly connected to the neurostimulator via the extension leads, the proximal ends of the stimulation leads can be inserted into connectors located at the distal ends of the respective extension leads, such that the terminals of the stimulation leads are coupled to corresponding electrical contacts within the connectors of the extension leads. The proximal ends of the extension leads can then be inserted into the connector of the neurostimulator, such that terminals located at the proximal ends of the extension leads are coupled to the corresponding electrical contacts within the connector of the neurostimulator. Individual wires are routed though each extension lead to respectively couple the proximally-located terminals to the distally-located electrical contacts.
In the context of an SCS procedure, one or more stimulation leads are introduced through the patient's back into the epidural space under fluoroscopy, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array. The specific procedure used to implant the stimulation leads will ultimately depend on the type of stimulation leads used. Currently, there are two types of commercially available stimulation leads: a percutaneous lead and a surgical lead.
A percutaneous lead comprises a cylindrical body with ring electrodes, and can be introduced into contact with the affected spinal tissue through a Touhy-like needle, which passes through the skin, between the desired vertebrae, and into the epidural space above the dura layer. For unilateral pain, a percutaneous lead is placed on the corresponding lateral side of the spinal cord. For bilateral pain, a percutaneous lead is placed down the midline of the spinal cord, or two percutaneous leads are placed down the respective sides of the midline. In many cases, a stylet, such as a metallic wire, is inserted into a lumen running through the center of each of the percutaneous leads to aid in insertion of the lead through the needle and into the epidural space. The stylet gives the lead rigidity during positioning, and once the lead is positioned, the stylet can be removed after which the lead becomes flaccid.
A surgical lead has a paddle on which multiple electrodes are arranged in independent columns, and is introduced into contact with the affected spinal tissue using a surgical procedure, and specifically, a laminectomy, which involves removal of the laminar vertebral tissue to allow both access to the dura layer and positioning of the lead.
After proper placement of the stimulation leads at the target area of the spinal cord, the leads are anchored in place at an exit site to prevent movement of the stimulation leads. To facilitate the location of the neurostimulator away from the exit point of the stimulation leads, extension leads are sometimes used. In particular, the proximal ends of the stimulation leads, which include terminals respectively coupled to the electrodes on the stimulation leads, are inserted into connectors located at the distal ends of extension leads.
The proximal ends of the stimulation leads exiting the spinal column, or alternatively extension leads, are passed through a tunnel subcutaneously formed along the torso of the patient to a subcutaneous pocket (typically made in the patient's abdominal or buttock area) where a neurostimulator is implanted. The subcutaneous tunnel can be formed using a tunneling tool over which a tunneling straw may be threaded. The tunneling tool can be removed, the stimulation leads threaded through the tunneling straw, and then the tunneling straw removed from the tunnel while maintaining the stimulation leads in place within the tunnel.
The stimulation leads are then connected to the neurostimulator, which can then be operated to generate electrical pulses that are delivered, through the electrodes, to the targeted tissue, and in particular, the dorsal column and dorsal root fibers within the spinal cord. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. During the surgical procedure, the neurostimulator may be operated to test the effect of stimulation and adjust the parameters of the stimulation for optimal pain relief. The patient may provide verbal feedback regarding the presence of paresthesia over the pain area, and based on this feedback, the lead positions may be adjusted and re-anchored if necessary. Any incisions are then closed to fully implant the system.
After the system is fully implanted, it is important that the subcutaneously implanted components, such as the neurostimulator and extension leads, be of a low-profile nature for aesthetic reasons as well as to prevent or minimize any discomfort of the patient that may otherwise occur by having rigid objects that do not conform to the natural curvature and movement of the patient.
However, in order to accommodate the present-day contacts, which either take the form of metal collars containing set screws or contacts or biasing mechanisms that frictionally engage the lead as it is introduced into the connector, the connectors of the extension lead and adapter are typically larger and stiffer than the bodies of the extension lead and adapter, thereby increasing the overall profile, while decreasing the conformity, of the extension lead and adapter.
In addition, in order to firmly secure the terminals of a lead within a connector (e.g., the terminals of the stimulation lead within the connector of an extension lead or neurostimulator, or the terminals of the extension lead within the connector of the neurostimulator), a special tool, such as a relatively expensive torque wrench, is typically used to tighten (within a predetermined tolerance range) at least one set screw that is either associated with each of the contacts or one end of the connector. The requirement of tools outside of the surgeon's normal practice increases the likelihood of their incorrect use with the lead system as well as increasing the time required to correctly complete the implantation procedure. These factors may decrease the effectiveness of the therapy or increase the possibility of patient injury.
Additionally, problems associated with maintaining sufficient electrical coupling between the contacts of the connector and the terminals of the lead can result in intermittent or failed connection to the lead, resulting in a failure in the intended therapy. Also, the use of set screws may mar the surface properties of the contacts rendering the entire implanted system at risk of complete removal. Furthermore, contacts that utilize biased friction mechanisms as an alternative to set screws may have relatively high insertion forces that prevent frictionless insertion of the lead into the connector, which may limit the number of lead insertions and withdrawals for the connector head or result in the clinician damaging the lead during its insertion into the connector. These contacts may also be relatively expensive, which given the number of contacts required, may result in a connector that is prohibitively expensive
There, thus, remains a need for an improved connector for an electrical lead assembly.